How To? - Use Javascript To Test If a TextBox Exists On a Page

[joey.powell]

I have a home page with username and password textboxes and a login
button for purposes of users being able to log in (forms
authentication) directly on the site home page. I also have a dedicated
"Login.aspx" page, but I don't want users redirected there unless
absolutely necessary.

I have registered a javascript block via "Page.RegisterStartupScript"
that sets focus to the "txtUserName" textbox control on Page Load. It
works great for IE and Firefox.

But...

The problem is that the "txtUserName" textbox does not exist once the
user has logged in and the page posts back. The code behind then knows
that the user is authenticated, and so it does a ".Visible=false" for
the "txtUserName", "txtPassword" and "btnLogin" controls.

Then, when the page loads after the postback, the javascript block
causes an error icon in the lower left corner of the browser.
Apparently it is still trying to set focus to the control? I thought I
had this fixed when I set the code behind to register the page startup
script only when the page loaded for the first time...but that didn't
work for some reason, because it still tries to set focus on postbacks.
I also tried disabling the page viewstate along with the above, but
that didn't work either.

Can the javascript block be coded to test if the "txtUserName"
(document.txtUserName ?) textbox exists before trying to set focus to
it? If so then that would do it...but how would the code look? Also, is
there another solution that I am not seeing here? I need to get this
working correctly.

Any suggestions are appreciated. Thanks.

 

[Guest]

I am not sure what the actual problem is. I understand what you are trying to
do, but not the why you are trying to do it.

Is the problem, there are certain pages that a user should not have to log
in to use? If so, restrict those pages by turning authentication off for
those pages. You set up a separate section of the web.config to exclude those
pages. Conversely, you can restrict the small number of login pages, if they
are fewer.

Is the problem, depending on how a user gets into the app they may be
authenticated by the network. If so, set up the login cookie when you find
those types of users and they will never be redirected to the login.aspx page.

What am I getting at? You are asking how to do something that is rather
kludgy and it is more likely you are doing this out of a misunderstanding of
how ASP.NET authentication works rather than a real need to do it this way.
By rephrasing the why, you might find that you do not have to go to the
trouble of adding JavaScript to the login page to hide controls from the user.

--
Gregory A. Beamer
MVP; MCP: +I, SE, SD, DBA

***************************
Think Outside the Box!
***************************

 

[joey.powell]

Gregory, I think it is you that does not understand. While I know that
I have a lack of understanding about some things in asp.net (like
everyone else?), I am fairly confident that I do not have a
misunderstanding!

In my original post I never said anything about using javascript to
hide controls...that would not make any sense here. Maybe I just worded
it in a confusing way...if so then I am sorry.

I am only using javascript to set focus to my txtUserName textbox. The
hiding of controls is occuring in the code behind once the user logs
in, as it should. The problem is that the javascript continues to try
to set focus once the page does a post back and the controls are hidden
(null). This generates the error. I simply wanted a javascript sample
that could be used to test for the controls on the page before
attempting to set focus.

I think that Eliyahu's post above will do just that.

Anyways, thanks a bunch to both of you!

JP>

 

[Eliyahu Goldin]

var txtBox=document,getElementById( "txtUserName");
if (txtBox!=null)
txtBox.focus();


Eliyahu

 

[Guest]

You can also do

if(typeof(txtUserName) != "undefined")
txtBox.focus();

Sreejith

 

[Guest]

Ideally, you should remove the scripts that are not needed for the current
execution of the page.

On page_load, if the request is a not a postback, attach the scripts to the
startup for the textbox focus. If the request is a postback, then don't
attach the scripts.
--
Direct Email: Michael.Baltic@RemoveCharactersUpTo#NCMC.Com

Staff Consultant II
Enterprise Web Services
Cardinal Solutions Group

 

[joey.powell]

I agree with totally...and I tried that. I put the
Page.RegisterStartupScript code line within the "if(!Page.IsPostBack)
block. However, that did not work for some reason. The script continued
to be emitted within the HTML for postbacks. I am not sure why.

But, I did get it working properly. Thanks.

 

[Eliyahu Goldin]

I never liked the idea of attaching scripts from the server code. If the
script is short, you won't feel any difference if it or there or not. If it
is long, say more then 20 lines of code, you can put it in a separate file
that will be cached on client side.

Eliyahu

 

[catherine sea]

Thank you, Eliyahu. It helps.